The subject matter of the present invention relates to perforating guns used in oil well boreholes, and, more particularly, to a perforating gun having rotating charges for positioning charges prior to detonating the charges.
Rotating charge perforating guns of the prior art possessed several problems which created a need for the subject invention. For example, springs were required for each charge thereby limiting the size of a perforating charge which could be packaged within a limited gun diameter. Since penetration into a formation is of prime importance and since penetration is a function of the size of a charge, the performance of prior art designs is inferior to the performance of the subject invention. Prior art rotating charge perforating guns deployed charges in series, creating a reliability problem from the standpoint of gun deployment. For example, the prior art rotating charge guns (Swing Guns) deployed the charges in series with an initial torque of 13.5 in-lb which decreased to less than 5 in-lb in the fully deployed position. If one charge failed to deploy, all remaining undeployed charges could not deploy nor could the gun be fired. The Swing Guns were 10 feet long with 41 charges. If the reliability of deployment was 99.5%, per charge, the gun had a 81.4% chance of fully deploying and firing. If the reliability of deployment was 95% per charge, the gun only had a 12.2% chance of ever firing. The swing gun design of the prior art was very sensitive and did experience deployment reliability problems. In addition, relative motion between the charge primacord and the charge itself, during deployment of prior art guns, sometimes caused charge misfires. Since pivots were exposed to the external surface of the gun carrier, rubbing of the gun carrier against the oil well tubing damaged the pivots and the other small mechanical parts which compromised the deployment of charges of the prior art. Furthermore, the swing gun of the prior art contained 82 pivots screwed into the charge cases, with pivot heads flush with the carrier. These exposed pivots caused the swing gun to stick inside the tubing. This problem was especially evident when the charges were deployed and not fired. In retrieving an unfired swing gun, the charges were spring loaded into the deployed position and rubbed against the tubing. If any one pivot worked loose, the gun became stuck inside the tubing. Furthermore, rotating charge perforating guns of the prior art have an inherent conflict in design. Prior art perforating guns only rotated or only translated the charges during deployment, not both. It is highly desirable that the charges both rotate and translate during deployment, because the perforating charge needs to be as large as possible to maximize the perforating performance while the mechanical mechanism needs to be strong and rugged enough to reliably deploy the charges in a hostile environment deep in an oil or gas well. However, strong mechanical linkages take space and reduce the size of the perforating charge in the gun. Therefore, a compromise was always made on prior art perforating guns between charge size and deployment strength, and, indirectly, between charge size and deployment reliability.